Medical imaging technologies have a recurrent history of diffusing into routine marketplace use before validation through a scientifically sound technology assessment. For example, over the last 25 years, if and how to use computer tomography and subsequent magnetic resonance imaging of various anatomic sites and patient symptoms occurred in an expensive, chaotic manner. Much of this chaos could have been avoided if Health Care Quality & Effectiveness Research SS HILLNER, BRUCE E. prospective, methodologically rigorous studies had occurred in advance of widespread adoption of these technologies. It is likely that a repeat of this history will occur with Positron Emission Tomography (PET) scanning. Although a randomized assessment of PET scanning is no longer feasible in the U.S., critically important information on how PET scanning is used in practice can be learned using an appropriate study design. The proposed pilot project involving a single academic health center setting will assess probability estimates and actions of the referring physicians. Future applications intend to extend the concept to a multi-site consortium and potentially include a linkage to claims and survival data of the patients undergoing PET scans at the consortium sites. The pilot study will collect questionnaire data from referring physicians twice: (1) before a PET scan is performed as part of the ordering process and (2) after completion and reporting of the PET scan (about one week later). The endpoints to be measured are: 1) The size and direction of change in the physician?s probability estimate (pre vs. post) of either the presence of cancer, the stage, resectability or recurrence of cancer; 2) The change in the physician?s intended patient management plan given the PET scan results; 3) The frequency of unexpected upstaging (areas of suspected cancer not previously noted) that may or may not alter patient management; 4) The frequency rate at which these unexpected areas of suspected cancer are pathologically confirmed.